V4L/DVB (6275): V4L: vivi.c remove the "resource" locking

The "resource" locking in vivi isn't needed since
streamon/streamoff/read_stream do mutual exclusion using
q->reading/q->streaming.

Plus it is sort of broken:

a) res_locked() use in vivi_read() is racey.
b) res_free() calls mutex_lock twice causing streamoff to break

Signed-off-by: Brandon Philips <bphilips@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>